A combustion engine, such as a diesel engine, may involve injection of fuel, such as diesel fuel, into one or more cylinders of the engine for combustion. In addition to injection of fuel for combustion, fuel may be injected into one or more of the cylinders as a post combustion event with the intention that the fuel passes out of the cylinder or cylinders without oxidising. Such a technique may be useful when the combustion engine is used with an exhaust fluid treatment apparatus. This may allow for unburnt fuel to arrive in the exhaust fluid treatment apparatus. Unburnt fuel may oxidise in the exhaust fluid treatment apparatus which may be useful when there is a desire to increase the temperature in the exhaust fluid treatment apparatus or when there is a desire to burn off, for example, unburnt carbon in the form of soot which may collect in a diesel particulate filter of the exhaust fluid treatment apparatus.
There may be a requirement for the volume of unburnt fuel to be passed through the cylinder to be precise. There may be a limited time between combustion events for injection of fuel which is intended not to oxidise in the cylinder. In the event that the amount of fuel to be passed through the cylinder changes rapidly, there may be a desire for a smooth transition from a first rate of flow of fuel to a second rate of flow of fuel. In addition, there may be a desire to avoid fuel being injected towards the internal walls of the cylinder.
Against this background, there is provided a method of controlling fuel to be injected within a combustion engine.